As more and more efforts have been made in recent years for utilizing deep underground regions in urban areas, there have been trends towards rainwater discharge pump stations also installed in deep subterranean regions. A typical water-lifting pump apparatus for use in such rainwater discharge pump stations has a discharge valve and a check valve that are connected to a discharge side of the pump. FIG. 1 is a schematic view showing a conventional water-lifting pump apparatus for use in a deep subterranean discharge pump station. As shown in FIG. 1, the conventional water-lifting pump apparatus is of a general structure which includes a pump 300 having an suction piping 301 connected to a suction tank 310 and a discharge piping 303 connected to a discharge tank 330. The pump 300 is connected to an actuator 370 in the form of an internal combustion engine through a transmission (speed reducer) 350. The discharge piping 303 is provided with a check valve 305 and a discharge valve 307. When rain falls, the actuator 370 is driven to start operating the pump 300, thereby pumping the rainwater that has flowed into the suction tank 310 through the suction piping 301 and the discharge piping 303 into the discharge tank 310.
In the water-lifting pump apparatus, the discharge valve 307 is installed in the discharge piping 303 for the following reasons (1) through (3):
(1) Water in the discharge piping 303 and water in a downstream region (on the discharge tank 330 side) of the discharge piping 303 are prevented from flowing back when the pump is stopped or inspected for maintenance.
(2) With the discharge valve 307 being closed, the pump 300 is driven, and after the operation of the pump 300 is completed, the discharge valve 307 is gradually opened to reduce abrupt flow rate variations.
(3) The opening of the valve body of the discharge valve 307 is controlled to control the flow rate.
In the water-lifting pump apparatus, the check valve 305 is installed in the discharge piping 303 in order to prevent water in the discharge piping 303 and water in the downstream region (on the discharge tank 330 side) of the discharge piping 303 from flowing back in case of an emergency shutdown with the discharge valve 307 being open after the pump 300 has operated.
For reducing construction costs of deep subterranean discharge pump stations incorporating the above water-lifting pump apparatus, it is effective to reduce an amount of excavating civil work. In order to reduce an amount of excavating civil work, it is effective to place a pump, valves, and pipings in a compact layout in the pump station, thereby reducing a planar space required in the pump station. In the above discharge pump station, particularly, reducing the valves including the discharge valve 307 and the check valve 305 to make the required space compact is highly effective to reduce an amount of excavating civil work.
FIG. 2 is a schematic view showing another conventional water-lifting pump apparatus which is free of both an discharge valve and a check valve. Those parts of the water-lifting pump apparatus shown in FIG. 2, which are identical or equivalent to those shown in FIG. 1, are denoted by identical reference characters. The water-lifting pump apparatus shown in FIG. 2 differs from the water-lifting pump apparatus shown in FIG. 1 in that the discharge piping 303 has a siphonic piping 303a, rather than the check valve 305 and the discharge valve 307, with a siphon break valve 309 being connected to the crest of the siphonic piping 303a, and an actuator 370 in the form of an electric motor is used in place of the actuator 370 in the form of an internal combustion engine.
When the pump 300 is stopped (also in case of an emergency shutdown) or inspected for maintenance, the siphon break valve 309 is opened to introduce atmospheric air into the siphonic piping 303a of the discharge piping 303, causing a siphon break thereby to prevent water from flowing back in the discharge piping 303. In this water-lifting pump apparatus, when remaining water in the discharge piping 303 falls freely, the pump 300 rotates reversely at a high speed. Internal combustion engines (diesel engines, gas turbines, etc.) are not allowed to rotate reversely to a large extent. If internal combustion engines are reversed in the absence of any countermeasures, then they will be damaged by the. reversing torque. Therefore, the water-lifting pump apparatus employs, as the actuator 370, an electric motor that is free of mechanical problems due to the reversing operation.
However, using the electric motor as the actuator is more costly for the reason of general economic efficiency than using the internal combustion engine as the actuator because the electric motor needs a separate non-utility power generation facility in order to keep electric power in case of interruption of electric service.
In the water-lifting pump apparatus, water in discharge piping 303 falls freely, and the reverse flow in the pump 300 is not controlled. Therefore, the pump 300 and the actuator 370 rotate reversely freely. As the depth of the water-lifting pump apparatus installed is greater, i.e., as the pump head is greater and thereby the energy consumed is larger, the pump 30 and the pipings 301, 303, or the civil engineering structure associated with the pump 300, is excessively affected in the form of large vibrations. If they are affected much more greatly, then the components could be damaged. When the pump 300 and the actuator 370 are reversed and the water flows back in the discharge piping 303, the components produce excessive noise, making people feel uncomfortable and anxious.